Conventionally, as a light source of a backlight in a liquid crystal display device, and the like, a cold cathode fluorescent lamp (CCFL) is used. However, there are problems such that, when the cold cathode fluorescent lamp is applied as the light source of the backlight, a color reproducibility is poor, and an environmental burden is large since mercury is used. In recent years, there has been developed a light emitting diode (LED) such as a blue light emitting diode and an ultraviolet light emitting diode, and the application of illumination using the LED to the backlight, and the like, has been promoted.
As a method of forming an LED illumination, a method of combining a blue light emitting LED chip with a yellow phosphor, a method of mixing lights of the blue light emitting LED chip, a red light emitting LED chip, and a green light emitting LED chip, and a method of combining an ultraviolet light emitting LED chip (UV-LED) with an RGB phosphor which contains phosphors of three colors consisting of red, green, and blue, are known. Since the former two methods have problems in the color reproducibility, color adjustment, and the like, there is an increasing expectation for the use of the method in which the UV-LED and the RGB phosphor are combined.
The LED has a long operating life and high reliability, and when being used as a light source, its replacement works are reduced, so that it is expected to be used as a component part of various display devices. An LED chip is a semiconductor element which converts electric energy into lights such as ultraviolet light or visible light to emit the light, and an LED lamp is formed by sealing the LED chip with transparent resin. A luminescent color of the LED lamp depends not only on a light emission wavelength of the LED chip, and light in a visible range from blue to red according to an intended use can be obtained by coating a phosphor on a surface of the LED chip or by including a phosphor in the transparent resin sealing the LED chip. Particularly, a white light emitting LED lamp is expected as a light source of a backlight in a liquid crystal display device of in a portable communication device and a PC.
When the LED lamp is applied as the light source of the backlight, a light emitting module is structured by arranging a plurality of LED lamps on a substrate linearly or in a matrix shape. The backlight applying the light emitting module provided with the plurality of LED lamps is classified into a direct-type backlight and a sidelight-type backlight, depending on the arranged position of the light source, and these are used properly according to usage. The sidelight-type backlight is formed by arranging the light emitting module, as a light source, on a side surface to be an incident surface of a light guide plate (refer to Patent Reference 1).
However, in the backlight using the light emitting module, the method of combining the UV-LED and the RGB phosphor has problems such that a light emission efficiency is low, and the luminance differs between portions where the LED lamp is disposed and where it is not, resulting that the uniformity of luminance becomes less as a whole. Further, there is also a problem that the luminance of a light emitting surface becomes insufficient although a desired luminous flux is obtained from the respective LED lamps composing the light emitting module. As a method of eliminating such an insufficiency or nonuniformity of the luminance, it is conceivable to increase the number of LED lamps mounted in the light emitting module to increase the disposition density thereof, but, in this case, the power consumption is inevitably increased.    Patent Reference 1: JP-A 2000-258749 (KOKAI)